At present, struct device lacks a mechanism of exposing memory
access constraints for the device.
Consequently, there is also no mechanism to share these constraints
while sharing buffers using dma-buf.
If we add support for sharing such constraints, we could use that
to try to collect requirements of different buffer-sharing devices
to allocate buffers from a pool that satisfies requirements of all
such devices.
This is an attempt to add this support; at the moment, only a bitmask
is added, but if post discussion, we realise we need more information,
we could always extend the definition of constraint.
A new dma-buf op is also added, to allow exporters to interpret or decide
on constraint-masks on their own. A default implementation is provided to
just AND (&) all the constraint-masks.
What constitutes a constraint-mask could be left for interpretation on a
per-platform basis, while defining some common masks.
Signed-off-by: Sumit Semwal <sumit.semwal at linaro.org>
Cc: linux-kernel at vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: linux-media at vger.kernel.org
Cc: dri-devel at lists.freedesktop.org
Cc: linaro-mm-sig at lists.linaro.org
---
drivers/dma-buf/dma-buf.c | 50 ++++++++++++++++++++++++++++++++++++++++++-----
include/linux/device.h | 7 ++++++-
include/linux/dma-buf.h | 14 +++++++++++++
3 files changed, 65 insertions(+), 6 deletions(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index f3014c4..33bdb6a 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -264,6 +264,30 @@ static inline int is_dma_buf_file(struct file *file)
return file->f_op == &dma_buf_fops;
}
+/*
+ * def_calc_access_constraints - default implementation of constraint checking
+ */
+static int def_calc_access_constraints(struct dma_buf *dmabuf,
+ struct dma_buf_attachment *attach)
+{
+ unsigned long access_mask;
+
+ access_mask = attach->dev->dma_parms->access_constraints_mask;
+
+ if (!access_mask) {
+ pr_warn("%s dev has no access_constraints_mask; using
default\n",
+ dev_name(attach->dev));
+ access_mask = DMA_BUF_ALL_MEMORY_ACCESS_MASK;
+ }
+
+ dmabuf->access_constraints_mask &= access_mask;
+
+ if (!dmabuf->access_constraints_mask)
+ return -EINVAL;
+
+ return 0;
+}
+
/**
* dma_buf_export_named - Creates a new dma_buf, and associates an anon file
* with this buffer, so it can be exported.
@@ -313,6 +337,8 @@ struct dma_buf *dma_buf_export_named(void *priv, const
struct dma_buf_ops *ops,
dmabuf->ops = ops;
dmabuf->size = size;
dmabuf->exp_name = exp_name;
+ dmabuf->access_constraints_mask = DMA_BUF_ALL_MEMORY_ACCESS_MASK;
+
init_waitqueue_head(&dmabuf->poll);
dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;
@@ -410,8 +436,10 @@ void dma_buf_put(struct dma_buf *dmabuf)
EXPORT_SYMBOL_GPL(dma_buf_put);
/**
- * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
- * calls attach() of dma_buf_ops to allow device-specific attach functionality
+ * dma_buf_attach - Add the device to dma_buf's attachments list;
+ * calculates access_constraints and throws error if constraints aren't
+ * satisfied. Optionally, calls attach() of dma_buf_ops to allow
+ * device-specific attach functionality.
* @dmabuf: [in] buffer to attach device to.
* @dev: [in] device to be attached.
*
@@ -436,11 +464,20 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf
*dmabuf,
mutex_lock(&dmabuf->lock);
+ if (!dmabuf->ops->calc_access_constraints)
+ ret = def_calc_access_constraints(dmabuf, attach);
+ else
+ ret = dmabuf->ops->calc_access_constraints(dmabuf, attach);
+
+ if (ret)
+ goto err_attach;
+
if (dmabuf->ops->attach) {
ret = dmabuf->ops->attach(dmabuf, dev, attach);
if (ret)
goto err_attach;
}
+
list_add(&attach->node, &dmabuf->attachments);
mutex_unlock(&dmabuf->lock);
@@ -785,7 +822,7 @@ static int dma_buf_describe(struct seq_file *s)
return ret;
seq_puts(s, "\nDma-buf Objects:\n");
- seq_puts(s, "size\tflags\tmode\tcount\texp_name\n");
+ seq_puts(s, "size\tflags\tmode\tcount\tconstraints\texp_name\n");
list_for_each_entry(buf_obj, &db_list.head, list_node) {
ret = mutex_lock_interruptible(&buf_obj->lock);
@@ -796,10 +833,11 @@ static int dma_buf_describe(struct seq_file *s)
continue;
}
- seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\n",
+ seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%08lx\t%s\n",
buf_obj->size,
buf_obj->file->f_flags, buf_obj->file->f_mode,
(long)(buf_obj->file->f_count.counter),
+ buf_obj->access_constraints_mask,
buf_obj->exp_name);
seq_puts(s, "\tAttached Devices:\n");
@@ -808,7 +846,9 @@ static int dma_buf_describe(struct seq_file *s)
list_for_each_entry(attach_obj, &buf_obj->attachments, node) {
seq_puts(s, "\t");
- seq_printf(s, "%s\n", dev_name(attach_obj->dev));
+ seq_printf(s, "%s\t:%lx\n",
+ dev_name(attach_obj->dev),
+ attach_obj->dev->dma_parms->access_constraints_mask);
attach_count++;
}
diff --git a/include/linux/device.h b/include/linux/device.h
index a608e23..f9aefa2 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -647,6 +647,11 @@ struct device_dma_parameters {
*/
unsigned int max_segment_size;
unsigned long segment_boundary_mask;
+ /*
+ * access_constraints_mask: this would be used to share constraints
+ * about memories that this device can access.
+ */
+ unsigned long access_constraints_mask;
};
struct acpi_device;
@@ -696,7 +701,7 @@ struct acpi_dev_node {
* such descriptors.
* @dma_pfn_offset: offset of DMA memory range relatively of RAM
* @dma_parms: A low level driver may set these to teach IOMMU code about
- * segment limitations.
+ * segment limitations, and access constraints.
* @dma_pools: Dma pools (if dma'ble device).
* @dma_mem: Internal for coherent mem override.
* @cma_area: Contiguous memory area for dma allocations
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 694e1fe..8429a38 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -37,6 +37,8 @@ struct device;
struct dma_buf;
struct dma_buf_attachment;
+#define DMA_BUF_ALL_MEMORY_ACCESS_MASK ((unsigned long)-1)
+
/**
* struct dma_buf_ops - operations possible on struct dma_buf
* @attach: [optional] allows different devices to 'attach' themselves to the
@@ -44,6 +46,12 @@ struct dma_buf_attachment;
* is already allocated and incompatible with the requirements
* of requesting device.
* @detach: [optional] detach a given device from this buffer.
+ * @calc_access_constraints(): [optional] will be called at the end of each
+ * attach - to calculate and set the constraints for this dma_buf
+ * according to this attachment's access_constraint_mask in
+ * dev->dma_parms.
+ * A default implementation is provided, but exporters are free to
+ * provide custom version if needed.
* @map_dma_buf: returns list of scatter pages allocated, increases usecount
* of the buffer. Requires atleast one attach to be called
* before. Returned sg list should already be mapped into
@@ -77,6 +85,9 @@ struct dma_buf_ops {
void (*detach)(struct dma_buf *, struct dma_buf_attachment *);
+ int (*calc_access_constraints)(struct dma_buf *,
+ struct dma_buf_attachment *);
+
/* For {map,unmap}_dma_buf below, any specific buffer attributes
* required should get added to device_dma_parameters accessible
* via dev->dma_params.
@@ -86,6 +97,7 @@ struct dma_buf_ops {
void (*unmap_dma_buf)(struct dma_buf_attachment *,
struct sg_table *,
enum dma_data_direction);
+
/* TODO: Add try_map_dma_buf version, to return immed with -EBUSY
* if the call would block.
*/
@@ -116,6 +128,7 @@ struct dma_buf_ops {
* @ops: dma_buf_ops associated with this buffer object.
* @exp_name: name of the exporter; useful for debugging.
* @list_node: node for dma_buf accounting and debugging.
+ * @access_constraints_mask: mask to share access constraints.
* @priv: exporter specific private data for this buffer object.
* @resv: reservation object linked to this dma-buf
*/
@@ -130,6 +143,7 @@ struct dma_buf {
void *vmap_ptr;
const char *exp_name;
struct list_head list_node;
+ unsigned long access_constraints_mask;
void *priv;
struct reservation_object *resv;
--
1.9.1
